Recombinant adenoviruses are currently used for the delivery of therapeutic transgenes in a variety of therapeutic regimens. However, the broad range of infectivity of these vector systems has raised concerns that the expression of the virus in non-tumor cells might cause collateral damage to non-neoplastic cells. Consequently, a broad range of targeting systems have been developed to preferentially express the transgene in a given cell type. Tissue specific and tumor specific promoters have been employed to preferentially replicate the vector in certain cell types. For example, International Patent Application No. PCT/US96/10838 published Jan. 16, 1997 (International Publication No. WO97/01358) describes the use of vectors which replicate in a specific host cell by the use of prostate specific promoter elements driving the E1, E2 or E4 functions, optionally containing a cytotoxic transgene expression cassette. In particular, this publication describes a construct where prostate specific enhancer controls expression of E1 and has a expression cassette comprising the CMV-promoter driving expression of the cytosine deaminase gene which is inserted into the E3 region. These vectors are replication competent and are capable of packaging into intact virions in a particular cell type.
An alternative approach to the use of tumor specific promoters to drive viral replication is to employ specific deletions in the adenoviral E1b 55K protein coding sequence. Recombinant adenoviruses which contain defects in the nucleotide sequence encoding E1b 55K are described in U.S. Pat. No. 5,677,178 issued Oct. 14, 1997. However, these tissue or tumor specific control elements have been observed to be “leaky”, i.e. permitting replication in cell types other than the preferred target cells.
Alternative to this type of selectively replicating vector is the employment of a replication deficient adenoviral vector containing extensive elimination of E1 function. In particular, vectors containing elimination of E1, E2 E3 and partial E4 deletions have been employed to delivery exogenous transgenes. Such vectors have been employed to deliver the p53 gene to target cells. It has been demonstrated that the expression of an exogenously administered wild type p53 in a p53 deficient (p53 mutated or p53 null) tumor cell is capable of inducing p53 mediated apoptosis in the tumor cell. Such viral vectors for the delivery of p53 are currently under development Schering Corporation and Introgen Corporation. Again these vectors have demonstrated acceptable toxicology profiles and therapeutic efficacy for human therapeutic applications and are in Phase II clinical trials in man for the treatment of p53 related malignancies.
Replication deficient and selectively replicating vectors have, at least in theory, design drawbacks which are of concern to clinicians. Because replication deficient vectors will not propagate uncontrollably in the patient, they theoretically have a more appealing safety profile. However, as effective tumor elimination requires the infection of the substantial majority of the tumor cells being infected, a substantial molar excess of vector is commonly used to insure therapeutic effectiveness. Selectively replicating vectors are viewed as being more of an issue from a safety perspective because of their ability to replicate and potentially mutate to form fully replication competent vectors in the patient. However, by maintaining the natural ability to the virus to propagate under particular conditions enables these vectors to spread to surrounding tumor cells. Since the vectors themselves are able to replicate, a lower initial dose of such vectors is required. This is favorable from an immunological perspective as well as for economic reasons in the manufacture of such agents. Therefore, there is a need in the art for a selectively replicating vector which addresses the perceived safety problems while providing the increased therapeutic index.
The present invention solves these problems by providing a selectively replicating adenoviral vector containing a pathway targeted pathway-responsive promoter driving expression of a repressor of viral replication such that the vector replicates preferentially in cells defective in the pathway. The present invention also provides pharmaceutical formulations comprising such vectors. The present invention also provides methods of eliminating pathway defective cells from a population of normal cells by using such vectors.